CVE-2025-1695: NGINX Unit Infinite Loop Vulnerability in Java Language Module - A Deep Dive

CVE-2025-1695 is a vulnerability found in the NGINX Unit application server that has the potential to cause a Denial-of-Service (DoS) attack. The issue was detected in the Java Language Module of NGINX Unit before version 1.34.2. This vulnerability can lead to an infinite loop, causing a spike in CPU resource utilization, and ultimately lead to a limited denial-of-service (DoS). To clarify, this vulnerability only affects the data plane and does not expose the control plane.

This post will delve into the details of CVE-2025-1695, including the code snippet responsible for the issue, links to official reports, and a step-by-step guide on how an attacker could exploit this vulnerability.

Official References

1. CVE-2025-1695 - NVD Details
2. NGINX Unit Security Advisory
3. NGINX Unit 1.34.2 Release Notes

Affected Code Snippet

NGINX Unit utilizes Java's java.nio.channels.SocketChannel class and its associated read function to handle incoming requests. The issue arises when a specific sequence of undisclosed requests is sent to the vulnerable NGINX Unit Java module. This sequence causes the read function to be stuck in an infinite loop, consuming CPU resources. Here's a simple representation of the affected code in the Java Language Module:

import java.nio.channels.SocketChannel;
import java.nio.ByteBuffer;
...
public class RequestHandler {
    public void processRequests(SocketChannel socketChannel) {
        ByteBuffer buffer = ByteBuffer.allocate(1024);

        try {
            while (true) {
                int bytesRead = socketChannel.read(buffer);
                if (bytesRead < ) {
                    // SocketChannel has reached an end-of-stream
                    break;
                } else {
                    // Process the read data and prepare for the next read
                    buffer.flip();
                    // [ OMITTED - Request processing ]
                }
            }
        } catch (IOException e) {
            // Handle I/O Exception
        }
    }
}

Exploiting the Vulnerability

A remote attacker can exploit this vulnerability by sending a series of undisclosed requests that initiate the infinite loop, thereby hogging CPU resources and causing the server to become unresponsive. Since it is a data plane issue, an attacker does not require access to the control plane to carry out this exploit.

Mitigation

To mitigate this vulnerability, it is critical to update your NGINX Unit installation to version 1.34.2 or later. This latest release contains an important fix that addresses the infinite looping issue within the Java Language Module.

Update instructions can be found at the official NGINX Unit Documentation.

Conclusion

CVE-2025-1695 is a critical vulnerability that affects the Java Language Module in NGINX Unit before version 1.34.2. By triggering an infinite loop in the request-processing code, an attacker can effectively perform a limited denial-of-service attack. Updating to the latest version of NGINX Unit (1.34.2) or higher is the recommended course of action to mitigate this issue. Stay vigilant and make sure your systems are up-to-date to ensure the security and stability of your deployments.

Timeline

Published on: 03/04/2025 01:15:10 UTC
Last modified on: 04/10/2025 18:55:19 UTC